Image illumination and capture in a scanning device

ABSTRACT

Scanning devices and method of use that permit the capture of high resolution images of an original that is illuminated by a light source that is located outside of the optical field of view of an image detector. In one aspect, the image detector may be a monochrome sensor that sequentially captures different color plane images of an original that is illuminated by different colors. The different color plane images may be processed to generate a full color copy of the original. Light and images may be directed through tapered optical waveguides to minimize the volume of the scanning device. The image detector may include a first associated waveguide while the light source may include a second associated waveguide.

CROSS REFERENCES TO RELATED APPLICATIONS

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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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REFERENCE TO SEQUENTIAL LISTING, ETC

None.

BACKGROUND

1. Field of the Invention

The present invention relates generally to scanners and scanningmethods, and more particularly to those permitting the capture of highresolution images of an original that is illuminated by a light sourcethat is located outside of the optical field of view of an imagedetector.

2. Description of the Related Art

Scanning devices are used in a variety of applications. Scanning devicesmay be combined in an all-in-one unit that includes scanning, printing,and facsimile function. Scanning devices may also be independent andonly capable of scanning documents. Historically, scanning devicesinclude a drive mechanism that moves a scan bar across a targetdocument. Each line of the document is individually scanned and the datais downloaded to a processor. This data is combined together to form afinal two dimensional image of the document. These scanning devicesrequire precise movement of the scan bar to prevent registrationdefects. Quality scans require intricate mechanisms which are oftencostly and complex.

Scanning devices, either of the all-in-one or independent variety, arepopular for both business and personal use. Ideally, the devices aredesigned to have a smaller size that enables placement within smallworkspaces such as desk tops and bookshelves. As a result, size is oftenan important aspect when deciding to purchase a scanning device. Smallerdevices are usually more accepted because of the ability to fit whereneeded and occupy a minimum space. Along with size, the price of thedevice is another important aspect during purchase. A device meetingother requirements may not be acceptable because of an higher price.

Digital photography technology has progressed with imaging units nowable to produce high quality two dimensional images in a single capturestep. Image sensors including millions of light sensors are readilyavailable. The imaging units are also economical allowing them to beutilized in new applications, such as document scanning technology. Theimaging unit includes a substantial field of view that is visible by theimage sensor. Thus, the imaging unit is able to capture most or all of adocument original. Unfortunately, the relatively large field of viewcreates space and illumination complications. The image sensor mayinclude a relatively large focal length. Further, stray reflections maybe prone to enter the field of view and reach the sensor. Accordingly,scan devices incorporating these types of imaging units shouldaccommodate these problems.

SUMMARY

The present application is directed to embodiments of scanning devicesand method of use that permit the capture of high resolution images ofan original that is illuminated by a light source that is locatedoutside of the optical field of view of an image detector. The lightsource may include individually selectable colors, such as red, green,and blue LEDs. In one aspect, the image detector may be a monochromesensor that sequentially captures different color plane images of anoriginal that is illuminated by different colors. The different colorplane images may be processed to generate a full color copy of theoriginal. Light and images may be directed through tapered opticalwaveguides to minimize the volume of the scanning device. The imagedetector may include a first associated waveguide while the light sourcemay include a second associated waveguide. In one embodiment, the firstwaveguide may be disposed between the second waveguide and a scan bed onwhich the original is positioned.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is perspective view of a scanning device according to oneembodiment of the present invention;

FIG. 2 is a block diagram of a scanning device according to oneembodiment of the present invention;

FIG. 3 is a schematic view of a scanning device illustrating a lightsource disposed outside of an sensor field of view according to oneembodiment of the present invention;

FIG. 4 is a schematic view of a scanning device illustrating a lightsource disposed at an acute angle relative to a scan bed according toone embodiment of the present invention;

FIGS. 5A-C are schematic views of a scanning device depicting a sequenceby which a scan bed is illuminated by different colors according to oneembodiment of the present invention;

FIG. 6 is a flow diagram depicting processing steps by which an originalis illuminated and captured with different colors and processed togenerate a duplicate according to one embodiment of the presentinvention;

FIG. 7 is a schematic view of a light source including an array of red,green, and blue sources according to one embodiment of the presentinvention;

FIG. 8 is a schematic view of a light source intensity control circuitaccording to one embodiment of the present invention;

FIG. 9 is a schematic view of a scanning device illustrating a lightsource disposed at an acute angle relative to a scan bed according toone embodiment of the present invention;

FIG. 10 is a schematic view of a tapered waveguide used in capturing animage according to one embodiment of the present invention;

FIG. 11 is a schematic view of a scanning device illustrating separatetapered waveguides for a light source and an imaging unit according toone embodiment of the present invention;

FIG. 12 is a schematic view of a tapered waveguide used with a lightsource according to one embodiment of the present invention; and

FIG. 13 is a schematic view of a scanning device illustrating separatetapered waveguides for a light source and an imaging unit according toone embodiment of the present invention.

DETAILED DESCRIPTION

The present application discloses embodiments for using an imaging unitwithin a scanning device. The scanning device includes an imaging unitand a target bed for placement of the target document. The scanningdevice may include an illumination system that limits an amount of straylight that reaches an image sensor. Further, the scanning device mayinclude a compact optics package that accommodates image sensors withlengthy focal lengths in a relatively small volume.

Spatially relative terms such as “under”, “below”, “lower”, “over”,“upper”, and the like, are used for ease of description to explain thepositioning of one element relative to a second element. These terms areintended to encompass different orientations of the device in additionto different orientations than those depicted in the figures. Further,terms such as “first”, “second”, and the like, are also used to describevarious elements, regions, sections, etc and are also not intended to belimiting. Like terms refer to like elements throughout the description.

As used herein, the terms “having”, “containing”, “including”,“comprising” and the like are open ended terms that indicate thepresence of stated elements or features, but do not preclude additionalelements or features. The articles “a”, “an” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

One embodiment of a scanning device is illustrated in FIG. 1 andindicated generally by the numeral 10. This embodiment features bothscanning and printing capabilities. Scanning device 10 comprises anexterior housing 12, a user interface 35, an imaging unit (not visiblein FIG. 1), at least one media input tray 14 adapted to hold a stack ofprint media, a media output tray 15, and a document handler 18. In oneembodiment, the document handler 18 is integrated into a cover 19 thatmay be lifted to expose a target bed (not visible in FIG. 1) on whichindividual target documents may be placed for subsequent scanning.Additional internal components for performing functions of printing andscanning are not visible in the exterior view illustrated in FIG. 1.

FIG. 2 provides a simplified representation of some of the variousfunctional components of the device 10 of FIG. 1. For instance, thedevice 10 includes an imaging unit 20 as well as a printing unit 60,which may itself include a conventionally known ink jet or laser printerwith a suitable document transport mechanism. Interaction at the userinterface 35 is controlled with the aid of an I/O controller 32. Thus,the I/O controller 32 generates user-readable graphics at a display 34and interprets commands entered at a keypad 36.

The device 10 may also include one or more processors 70, system memory71, which generically encompasses RAM and/or ROM for system operationand code storage as represented by numeral 72. The system memory 71 maysuitably comprise a variety of devices known to those skilled in the artsuch as SDRAM, DDRAM, EEPROM, Flash Memory, and perhaps a fixed harddrive. Those skilled in the art will appreciate and comprehend theadvantages and disadvantages of the various memory types for a givenapplication.

Additionally, the device 10 may include dedicated image processinghardware 64, which may be a separate hardware circuit, or may beincluded as part of other processing hardware. For example, control ofthe imaging unit 20 and of subsequent image processing may beimplemented via stored program instructions for execution by one or moreDigital Signal Processors (DSPs), ASICs or other digital processingcircuits included in the processing hardware 64. Alternatively, storedprogram code 72 may be stored in memory 71, with the control techniquesdescribed herein executed by some combination of processor 70 andprocessing hardware 64, which may include programmed logic devices suchas PLDs and FPGAs.

FIG. 2 also illustrates the imaging unit 20 including a sensor 21 andoptics 23. A light source 22 is also included to provide adequateuniform illumination for the original target document. Exemplary typesof sensors 21 may include CCD and CMOS sensors. Multilayer direct imagesensors may also be used. The optics 23 may comprise different types ofelements, such as some combination of mirrors, prisms, lenses, and beamsplitters. The optical lenses may be wide angle or telephoto lensesadapted to focus an image of an original document onto the sensor 21with minimum distortion or other optical aberrations. Other types oflenses may be used where appropriate.

Image sensors 21 that can be used include digital CMOS imaging modules,typically used in digital cameras, that currently are available invarious megapixels (MP) sizes and are available from manufacturers suchas Micron Technology, Inc., 8000 S. Federal Way, P.O. Box 6, Boise, Id.83707-0006 or Omnivision Technologies, Inc., 1341 Orleans Drive,Sunnyvale, Calif. 94089. As shown, these imaging modules will haveequivalent scan resolutions for 8.5×11 inch scanner and 4×6 inch scanner(typically used for scanning photographs) as summarized in Table 1.

TABLE 1 Imaging Sensor Size 8.5 × 11 Scanner 4 × 6 Scanner (MP)Equivalent Resolution Equivalent Resolution (4:3 aspect ratio) (ppi)(ppi) 1 102 192 2 144 272 3 176 333 4 204 385 5 228 430 6 250 471 7 270509 8 288 544 9 306 577 10 322 609The table illustrates that for a 200 pixel per inch resolution, a 4×6inch photo scanner can be designed with a 1 MP digital imaging sensorwhile an 8.5×11 inch scanner can use a 4 MP digital imaging sensor.

FIG. 3 illustrates one embodiment of an imaging unit 20 disposed withina scan device body 12 and configured to capture a digital representationof an original image positioned on a scan bed 17. The imaging unit 20includes a two-dimensional array of sensors 21 that “see” an image area30 on the scan bed 17. The sensors 21 in the imaging unit 20 include afield of view 32 that corresponds to the image area 30. Thus, the imagearea 30 extends in a direction substantially perpendicular to the pagein the orientation shown in FIG. 3. The illumination of a document orobject on the scan bed 17 needs to be done such that the image sensor 21only sees a desired object or image. The light source 22 should bepositioned so it does not become a part of the image that is beingcaptured. Further, reflections from the illumination sources 22 andsecondary reflections off the imaging unit 20 housing/lenses should beminimized. As part of the process of capturing digital representationsof an image on the scan bed 17, intensity, uniformity, and reflectionsshould also be addressed in the illumination system. To prevent thelight source 22 from appearing as a reflection in the image, the lightsource 22 is located outside of the field of view 32 of the document, asshown in FIG. 3.

The detail view provided in FIG. 4 shows that the light source 22projects light at an acute angle α to the scan bed 17. This directsreflected specular light 36 to the opposite side of the device body 12and does not reach the imaging unit 20. Meanwhile, diffuse light 34projects over a region of the image area 30. Notably, the angle α ofreflection also affects the illumination intensity. At too shallow of anangle α, the intensity may suffer while at too steep of an angle α,unwanted reflections may increase. In one embodiment, an angle α ofbetween about 15 and about 45 degrees may be appropriate though otherangles may be suitable for a given device 10 and imaging unit 20geometry.

The imaging unit 20 may include a color image sensor 21 or a monochromesensor 21. In certain implementations, systems using a color camera chipare adversely affected by the color masking that is typically used onthe sensor 21 chip to produce the full color image. Those skilled in theart will recognize that color camera chips are often masked with red,green, and blue colors in a Bayer pattern. The Bayer pattern is designedto replicate how the human eye sees color. The colors are distributed as25% red, 25% blue, and 50% green. When using the camera chip fordocument scanning, the premasked pattern results in a loss ofresolution.

A single pixel in an image sensor 21 can yield only intensityinformation about the light wavelengths that fall on it. Many colorimaging units 20 determine pixel color with a Bayer filter or otherfilters and interpolation from the intensity values of neighboringpixels. This interpolation inevitably reduces resolution. Further, thearrangement of blue and red pixel sites in a Bayer filter makes asingle-imager color camera prone to horizontal and vertical artifacts,especially on objects with straight edges that follow a row or column(common occurrences in document scanning). The Bayer pattern may alsocause artifacts at higher spatial frequencies. To obtain higherresolutions needed to scan a document, it is desirable to use everysensor 21 on the imaging unit 20.

To alleviate some of these problems, the device 10 may incorporate amonochrome sensor 21 with sequential color illumination. The monochromesensor 21 may distinguish between many shades of gray, ranging fromwhite to black. Different grayscale depths are known, including forexample, an 8-bit (256 shades) or greater sensor 21 may be used. Togenerate a color image, the monochrome sensor 21 may be used inconjunction with sequential RGB illumination. FIGS. 5A-C show that anoriginal positioned onto the scan bed 17 document is exposed todifferent colors in sequence and sampled using the monochrome fullsensor 21 array in the imaging unit 20. FIG. 6 also depicts exemplaryprocessing steps used in capturing separate color images and mergingthose images to obtain a full color duplicate. Specifically, in FIG. 5Aand at step 600, a first color source 22A illuminates the original andthe imaging unit 20 captures a first image. The monochrome imaging unit20 does not detect the color (e.g., hue, saturation, or chroma values).Instead, the imaging unit 20 captures an array of intensities detectedthrough illumination of the scan bed 17 by the first color source 22A.In FIG. 5B and at step 602, a second color source 22B illuminates theoriginal and the imaging unit 20 captures a second image. Next, in FIG.5C and at step 604, a third color source 22C illuminates the originaland the imaging unit 20 captures a third image. The first 22A, second22B, and third 22C color sources may comprise red, green, and blue LEDs.The light source 22 may be provided through other types of illuminationsources, including incandescent, fluorescent, fiber optics, or otherlight sources. Further, the order of color illumination may change asdesired.

At step 606, color processing may be implemented to the individualimages corresponding to each color or to a merged full color image.Since each color plane is individually captured, the exposure, gain,gamma correction, illumination, filtering, calibration, and color tablefor each color can be independently controlled for better colorfidelity. Further, since there are no moving parts in the system, motionerrors are substantially eliminated. Since, each color plane is capturedby the same pixels each time, the color planes may be merged at step 608to form a single, full color duplicate digital image of the imagepositioned on the scan bed 17. In one embodiment, the pixel intensitiesfrom the three image arrays are used as input values into a color tablethat may be stored in memory 71. The color table may includecorresponding color information needed to construct a full color image,resulting in a true color image that is at full resolution (i.e., usingsubstantially most or all pixels of the monochrome imaging unit).

In one embodiment, a 3.1 megapixel or higher imaging unit 20 is used.The array size for a conventional 3 megapixel sensor 21 is 2048×1536pixels, which reflects an aspect ratio of 4:3. One standard size sheetof paper has an aspect ratio of 11:8.5 (or 4:3.091). Since the ratiosare different, some pixels are lost or unused when capturing an 8.5″×11″image. Using the aspect ratio of a piece of paper, the pixel count thatmatches up with the camera sensor 21 would be 1988×1536 or 3053568pixels. This total represents a loss of 60×1536 or 92,160 pixels. Whentranslated to pixels per inch, the entire 8.5″×11″ image is captured at180.7 pixels per inch in the X and Y axis.

In one embodiment, the light source 22 includes red, green, and blueLEDs to illuminate the document (or object) on the flat bed 17. The LEDsshould be positioned in close proximity to illuminate the image with thesame uniformity for each color. Thus, the light source 22 may include anarray of individual LEDs, each being a different color as shown in FIG.7. In one embodiment, the LED's include red, green, and blue LEDs. Inone embodiment, the additional red LEDs are included in the array toincrease the luminance for the red channel. Additional red LEDs may beneeded due to a reduced sensitivity of the imaging sensors 21 in thespectrum of the red LEDs. Accordingly, the additional red LEDs mayprovide the needed additional luminance. In one embodiment, the imagesensor may include about twice as many red LEDs as blue or green LEDs.In one embodiment, groups of two red LEDs are positioned adjacent eachother, with the two adjacent red LEDs interspersed among green and blueLEDs.

FIG. 8 depicts a complementary or alternative approach that may be usedto adjust the intensity of individual LED colors. Specifically, thecontrol circuit 40 may provide additional intensity or luminance for agiven color. The exemplary control circuit 40 includes a simpleswitching transistor including a turn-on resistor 44 at the transistor42 gate. An LED 22 is disposed in line between a power source PWR andthe collector of transistor 42 and a variable resistor 46 is disposedbetween the emitter of transistor 42 and ground. When the transistor 42is turned on, current flows through the transistor 42 and the variableresistor 46 determines the voltage that appears at the LED. Thus, thevariable resistor 46 is adjustable to vary the intensity output by theLED 22. With this simple control circuit 40, the control of each coloris independent and allows for individual adjustment. It is comtemplatedthat the adjustment could be done automatically using circuitry and/orprogram instructions provided in device 10. Adjustment may also beimplemented as a function of LED position as much as LED color.

FIG. 9 shows one embodiment of a light source 22 used in conjunctionwith a reflector. In some instances, the length of the light path mayconsume a considerable amount of space. To reduce the area needed forillumination, a reflector 48 may be used to fold the light path andincrease space efficiency. One purpose of the reflector 48 is toredirect the light towards the scan bed 17. Thus, the reflector 48 mayinclude a polished, mirrored reflection surface 50. In one embodiment,the reflection surface may be configured to aid in the scattering of thelight to produce a more uniform distribution of light at the scan bed17. Accordingly, the reflection surface 50 may include a frosted,textured or white surface resulting in various amounts of diffusion atthe expense of reducing the intensity of the reflected light. Ingeneral, the reflector 48 offers a smaller size and allows flexibilityof diffusion materials, reflection angles, and light path. As describedabove and shown in FIG. 4, the reflector 48 should project light towardsthe scan bed 17 at an acute angle α. Notably, the diffuse light 34′ fromthe reflection surface 50 may project over a larger portion of the imagearea 30 as compared to the embodiment shown in FIGS. 3 and 4.

Additional space conservation for the light source 22 and the imagingunit 20 may be achieved through the use a tapered optical waveguide 80as shown in FIG. 10. A tapered optical waveguide device as described inUS Patent Application Publication 2004/0046870, incorporated byreference herein, is an apparatus in the form of a slab. Light from animage can be injected into a tapered surface, which in this case mayform a scan bed 17′, at a thin end 82 of the slab and then exits at theopposite thick end 83. The tapered scan bed 17′ is oriented such thatlight near the critical angle for the refractive index of the waveguide80 material enters the waveguide 80 and reflects internally along theslab towards the thick end 83. With this configuration, an originalimage (e.g., document or photo) is positioned on the scan bed 17′ at oneend 82 of the waveguide 80, and the imaging unit 20 is present at theopposite end 83. The focal length of the imaging unit 20 is measuredthrough the optical waveguide 80. One advantage of this method is thatthe space normally required to capture images with an imaging unit 20through air, is now contained within the waveguide 80. At the thick end83, of the waveguide 80, the slab extends for a length with parallelopposing faces 86, 88. The thickness between these faces 86, 88 of thewaveguide 80 is a function of the optical properties of the imaging unit20.

Notably, light may travel in both directions through waveguides 80 ofthis type. Accordingly, the scanning device 10 may incorporate a taperedwaveguide 80 to both illuminate an original with a light source 22 andcapture a digital image with an imaging unit 20. FIG. 11 illustrates oneexemplary embodiment of a scanning device 10 that includes a waveguide80 associated with each of the imaging unit 20 and the light source 22.In the embodiment shown, the imaging unit 20 includes a waveguide 80A,80B that is split into separate elements. An upper portion of thewaveguide 80A includes a tapered geometry as described above. A lowerportion of the waveguide 80B includes a substantially constantthickness. In essence, the split waveguide 80A, 80B is substantiallysimilar to the slab 80 shown in FIG. 10, with the waveguide 80A, 80Bfolded in half. The internally reflected light is folded 180 degrees byreflectors 90. The reflectors 90 may be implemented using mirrors, aprism, or other reflecting surfaces. A second waveguide 180 associatedwith the light source 22 is disposed between the folded halves of thewaveguide 80A, 80B associated with the imaging unit 20. Further, thethin ends 82, 182 of these waveguides 80A-B, 180 face substantiallyopposite directions so as to minimize the height of the device 10. Inthe embodiment shown, the light source 22 and imaging unit 20 aredisposed on the same side of the waveguides 80A, 80B, 180. However, inother embodiments, such as where the imaging unit 20 uses a waveguide 80that is not bent (such as in FIG. 13), the light source 22 and imagingunit 20 may be disposed on opposite sides of the waveguides 80, 180. Ineither case, light from light source 22 propagates towards the scan bed17 from a first direction D1 while the captured image propagates fromthe scan bed 17 towards the imaging unit 20 along an opposite seconddirection D2.

Light projected by the light source 22 travels down its associatedwaveguide 180 and escapes beneath the waveguide 80A associated with theimaging unit. This light from the light source 22 passes through thewaveguide 80A to illuminate the scan bed 17 as indicated by the verticalarrows L. Then, light reflected from the target image on the illuminatedscan bed 17 will enter the tapered upper portion of the waveguide 80A,pass around the reflectors 90, through the lower portion of thewaveguide 80B and ultimately reach the imaging unit 20. These waveguides80, 80A, 80B, 180 may be used with monochrome or color imaging units 20.

Light projected by the light source 22 may be further modified as shownin FIG. 12. The waveguide 180 may include a diffusion surface 185 at thetapered surface where light exits the waveguide 180. That is, thediffusion surface 185 is disposed at the surface where the slab tapersfrom the thick end 184 to the thin end 182. The waveguide 180 may alsoinclude an associated redirecting film 190 that bends the light emittedfrom the waveguide 180 in the direction of the scan bed 17 as shown bythe arrows L in FIG. 11. The redirecting film 190 may be constructed asa prismatic film as disclosed in US Patent Application Publication2006/0132423, the contents of which are incorporated by referenceherein. The result of the diffusion surface 185 and redirecting film 190is a uniform distribution of light over a large area but within a smallvolume. In different embodiments, the waveguide 180 may include one orboth or neither of the diffusion surface 185 and redirecting film 190.

As suggested above, the exemplary device 10 shown in FIGS. 1 and 2 mayinclude other components and other functionality. Certain copy or scanfunctions may be initiated at a user display 35, including a display 34.The display 34 may be embodied as an alphanumeric or graphical LCDdisplay and keypad 36 may be an alphanumeric keypad. Alternatively, thedisplay and input functions may be implemented with a composite touchscreen (not shown) that simultaneously displays relevant information,including images, while accepting user input commands by finger touch orwith the use of a stylus pen (not shown).

The exemplary embodiment of the device 10 also includes a modem 61,which may be a fax modem compliant with commonly used ITU and CCITTcompression and communication standards such as the V.XX and Class 1-4standards known by those skilled in the art. The device 10 may also becoupled to a computer or computer network (not shown) through acompatible communication port 62, which may comprise a standard parallelprinter port, a serial data interface such as USB 1.1, USB 2.0,IEEE-1394 (including, but not limited to 1394a and 1394b) and the like.

Device 10 may also include integrated wired or wireless networkinterfaces. Therefore, communication port 62 may also represent anetwork interface, which permits operation of the device 10 as astand-alone device. A wired communication port 62 may comprise aconventionally known RJ-45 connector for connection to a 10/100 LAN or a1/10 Gigabit Ethernet network. The wireless communication port 62 maycomprise an adapter capable of wireless communications with otherdevices in a peer mode or with a wireless network in an infrastructuremode. Accordingly, the wireless communication port 62 may comprise anadapter conforming to wireless communication standards such asBluetooth®, the various 802.11 standards, 802.15 or other standardsknown to those skilled in the art.

The present invention may be carried out in other specific ways thanthose herein set forth without departing from the scope and essentialcharacteristics of the invention. For instance, much of the discussionprovided herein has discussed the used of a monochrome image sensor thatcaptures multiple color plane images. It should be noted however, thatin the context of the waveguide light systems, the waveguides 80, 80A,80B, 180 may be used with monochrome or color imaging units 20. Thepresent embodiments are, therefore, to be considered in all respects asillustrative and not restrictive, and all changes coming within themeaning and equivalency range of the appended claims are intended to beembraced therein.

1. A scanning device comprising: a target bed; an imaging unit operativeto capture an image of a document placed on the target bed; a lightsource operative to illuminate the document placed on the target bed; atapered first slab waveguide configured to receive the image of thedocument into a first tapered face of the first slab, the imagepropagating through the waveguide from the first tapered face to a firstthick end of the first slab after internal reflection within the firstslab, the imaging unit disposed to receive the image as it emerges fromthe first thick end of the first slab; and a tapered second slabwaveguide configured to receive light from the light source into asecond thick end of the second slab, the light propagating through thewaveguide from the second thick end of the second slab and emerging froma second tapered face of the second slab after internal reflectionwithin the second slab, light from the light source transversely passingthrough the first slab to illuminate the document placed on the targetbed.
 2. The device of claim 1, wherein the light source comprises anarray of red, green, and blue light sources.
 3. The device of claim 1,wherein the first slab and the second slab are oriented so that thefirst thick end faces a substantially opposite direction from the secondthick end.
 4. The device of claim 1, wherein the first slab waveguideincludes a folded first portion and second portion with a reflectordisposed therebetween to fold the image from the first portion to thesecond portion, the first portion including the first tapered face, andthe imaging unit disposed to receive the image as it emerges from thesecond portion.
 5. The device of claim 4, the second slab waveguide isdisposed between the first and second portions of the first slabwaveguide.
 6. The device of claim 1, wherein the second slab waveguideincludes a diffuse second tapered face.
 7. The device of claim 1,further comprising a redirection element disposed at the second taperedface to redirect light towards the document placed on the target bed. 8.The device of claim 1, wherein the light source and imaging unit aredisposed on the same side of the first and second slab waveguides. 9.The device of claim 1, wherein the light source and imaging unit aredisposed on opposite sides of the first and second slab waveguides. 10.A method of scanning an image of a document with a scanning device, themethod comprising the steps of: positioning the document on a targetbed; illuminating the document using a light source and a tapered firstwaveguide, the light from the light source propagating through thetapered first waveguide; capturing an image of the document bypropagating the image of the document through a tapered second waveguideand towards an imaging unit; and causing the light from the light sourceto exit from a tapered surface of the first waveguide and transverselypass through the second waveguide, which is disposed between the firstwaveguide and the target bed.
 11. The method of claim 10, wherein thestep of illuminating the document using the light source and the taperedfirst waveguide comprises propagating the light along a first directionand the step of propagating the image of the document through thetapered second waveguide comprises propagating the image along a secondopposite direction.
 12. The method of claim 10, wherein the step ofilluminating the document using the light source comprises sequentiallyilluminating the document with different colors.
 13. The method of claim12, wherein the different colors comprise red, green, and blue.
 14. Themethod of claim 10, wherein the step of illuminating the document usingthe light source comprises redirecting the light between the taperedsurface of the first waveguide and the target bed.